The original series is fantastic and well worth watching. Advance Generation is pretty bad until Battle Frontier, and that's mostly because of how much repetitive filler there is and that just got annoying due to its formulaic nature. The original series also has a great dub when it comes to the voice acting - though the censorship is an issue.

The issue with Battle Frontier, though, is that midway through it, they switched to a fandub here in America, and the voice acting is unbearable. It's still mediocre in D/P's early stages, but D/P is actually a decent arc. B/W isn't that great because it's all battling, pretty much, and there isn't much character development, especially for a lot of the Pokemon. The fan voice actors have gotten a lot better with experience, however. Maybe the reason B/W isn't that good to me is because I've seen it all before, and they're doing nothing new with it. On its own, it might not be that bad...